Note: Descriptions are shown in the official language in which they were submitted.
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2-POSITION 3-WAY SOLENOID VALVE, MODULATOR
AND ANTI-LOCK BRAKE SYSTEM WITH THE VALVE
TECHNICAL FIELD
., 5
The present invention relates to a solenoid valve,
and a modulator and an anti-lock brake system with the
solenoid valve, more particularly to a 2-position 3-way
(hereinafter simply referred to as "2/3") solenoid valve
for an anti-lock brake system, a compact type of modulator
and an anti-lock brake system with the solenoid valve.
BACRGRO ~ D ART
lS Presently, an anti-lock brake system which prevents
wheels from locking while performing a braking operation
of a vehicle is widely utilized. If wheels are locked
during the braking operation to slip on a road surface, a
friction force between tires and the road surface is
reduced to lengthen the braking distance. The anti-lock
brake system repeatedly increases, holds or decreases the
braking pressure exerted on the wheels to impede the
locking of wheels. The increase of braking pressure is
generally referred to as an increase mode, the hold
thereof as a hold mode, and the decrease thereof as a
decrease mode. The anti-lock brake system is generally
composed of a pressure generating source, which is not a
master cylinder, for example, a pump and the like, valves
operated by an electrical signal, sensors for monitoring
a rotating speed of the wheels and a controller for
opening/closing the valves in accordance with a
predetermined algorithm for the purpose of acquiring an
effective braking operation.
FIG. lA is a schematic hydraulic circuit diagram for
35 showing a conventional anti-lock brake system utilizing 2-
position 2-way (hereinafter simply referred to as "2/2")
solenoid valves. In an increase mode, first and second
2/2 solenoid valves S220 and S 221 are de-energized to
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open first valve S220 connected to an outlet of a
hydraulic pump 120 and close second valve S221 connected
to an inlet of hydraulic pump 120, so that a hydraulic
pressure generated from hydraulic pump 120 is supplied to
brake wheel cylinder mounted to the wheels. In a hold
mode, first valve S220 is energized to close first valve
S220, so that the pressure of the brake wheel cylinder is
maintained constant. In a decrease mode, first and second
valves S220 and S221 are energized to close first valve
S220 and open second valve S221, so that the pressure of
the brake wheel cylinder is decreased. Such a system is
stably operated, but two solenoid valves per channel are
required. As a result, the utilized number of solenoid
valves is increased and the overall anti-lock brake system
becomes bulky.
FIG. lB is a schematic hydraulic circuit diagram for
showing a conventional anti-lock brake system utilizing 3-
position 3-way (hereinafter simply referred to as "3/3")
solenoid valves. In an increase mode, a 3/3 solenoid
valve S330 is de-energized, so that a hydraulic pressure
generated from a hydraulic pump 120 is supplied to the
brake wheel cylinder to increase the braking pressure. In
a hold mode, a primary switching signal is applied to 3/3
solenoid valve S330 to close all three ports thereof, so
that the pressure of the brake wheel cylinder is
maintained constant. In a decrease mode, a secondary
switching signal, of which the voltage is about twice that
of the primary switching signal, is applied to decrease
the pressure of the brake wheel cylinder. In such a
system, the utilized number of solenoid valves is
decreased, since a solenoid valve per channel is utilized.
However, the structure of solenoid valve is complicated,
the size thereof is large, an electronic control unit of
a complicated structure is required because of performing
2-step voltage control and the response time becomes long.
As a result, the system is operated unstably.
In order to overcome the foregoing problems, an anti-
lock brake system has been proposed as disclosed in U.S.
=
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Pat. No. 4,865,399 to Atkins et al. The system is
composed of a hydraulic pump, 2/3 solenoid valves allotted
to each wheel and a control means. ~owever, the system
doesn't overcome the foregoing problems completely, since
the number of valves utilized is not decreased enough,
i.e., the system further includes solenoid-operated
isolation valves as well as the 2/3 solenoid valves.
Therefore, the overall construction of the system is
complicated by utilizing a plurality of solenoid-operated
valves. Further, the construction of the 2/3 solenoid
valve utilized in the system is complex, whereby it is not
easy to ~abricate the valve.
Meanwhile, a 2/3 solenoid valve has been proposed as
disclosed in U.S. Pat. No. 5,135,027 to Nobuaki Miki et
al. However, the valve is not ~or an anti-lock brake
system but for a general-purpose hydraulic system. The
valve has the construction that a port is closed by the
movement of a ball caused by the flow of brake fluid, and
hence, the ball moves by the pressure difference. In
other words, the ball moves not by the movement of a
plunger but by the pressure difference between ports,
though electric power is applied to a solenoid coil to
move the plunger against the resilient force of a spring.
Therefore, if the pressure of an outlet port or an exhaust
port is higher than that of an inlet port, the valve
doesn't block a backward flow. Further, while a solenoid
valve for anti-lock brake system requires a response time
of 8 ms or below, the response time of the conventional
solenoid valve becomes long for the reason that the
movement of the ball is caused by the pressure difference
to operate the valve. Moreover, it is impossible that the
response time is kept constant, because of fluctuations of
the pressure difference of fluid.
DISCLOSURE OF INVENTION
The present invention is devised to solve the
foregoing problems. It is a first object of the present
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invention to provide a 2/3 solenoid valve being operated
rapidly, having a simple structure and high reliability
and being capable of controlling opening/closing
operations of the valve accurately.
It is a second object of the present invention to
provide a modulator having a simple structure and a small
size, wherein the modulator is for an anti-lock brake
system and is provided with the 2/3 solenoid valve.
It is a third object of the present invention to
provide an anti-lock brake system being constructed by
utilizing one 2/3 solenoid valve per channel.
To achieve the first object of the present invention,
there is provided a solenoid valve according to a first
embodiment comprising:
a valve body having a housing with a first port for
receiving fluid from a fluid generating source, a second
port for flowing in/flowing out the fluid and a third port
for exhausting the fluid, and a cover hermetically coupled
to one end of the housing for closing the one end of the
housing;
a barrier wall for partitioning a chamber surrounded
by the housing and cover within the valve body into first
and second chambers and having a first opening for
communicating the first chamber with the second chamber,
the first chamber being communicated with the first port
and the second chamber being communicated with the second
and third ports;
opening/closing means movable along lengthwise
direction of the valve body for alternatively opening and
closing the first opening and the third port in response
to an electric signal, and being positioned at a first
position of closing the third port and opening the first
opening in a normal state that the electric signal is not
applied or at a second position of closing the first
opening and opening the third port in an active state that
the electric signal is applied, whereby the first port is
communicated with the second port or the second port is
communicated with the third port; and
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a solenoid assembly having an annular solenoid coil,
a bobbin wound by the annular solenoid coil and a pair of
electrodes electrically connected to the annular solenoid
coil and exposed to the outside of the valve body for
moving the opening/closing means to the second position
from the first position in response to the electric
signal.
To achieve the first object of the present invention,
there is provided a solenoid valve according to a second
~0 embodiment further comprising an orifice for reducing the
fluctuation of hydraulic pressure through the second port
and a check valve preferably installed opposite to the
orifice for promptly reducing the hydraulic pressure
within the second chamber.
The opening/closing means, for example, comprises an
armature moving along the lengthwise direction in response
to a magnetic force generated by the solenoid assembly; a
cover spring, one end thereof supported on a closed end of
a hole formed in the center of a protrusion of the cover
and the other end thereof supported on the armature; a
spring supporting rod fixed to one end of the armature and
inserted in the cover spring to support the cover spring;
a push rod fixed to the other end of the armature; and a
spool integrally formed with the push rod, wherein the
cover, the spring supporting rod, the armature and the
push rod are included within the first chamber, the spool
is included within the second chamber, and the push rod
extends through the first opening to be connected to the
spool included within the second chamber.
Preferably, the barrier wall is formed by an inlet
nozzle, the third port is a second opening formed at an
outlet nozzle which is installed opposite to the inlet
nozzle, and the diameter of the first opening formed at
the inlet nozzle is larger than that of the push rod
passing through the first opening to provide a gap between
the first opening and the push rod, the gap communicating
the first chamber with the second chamber.
The first chamber is formed within the housing to be
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surrounded by the inlet nozzle, a protrusion formed in the
center of the cover and a cylindrical sealing member and
the second chamber is formed within the housing to be
surrounded by the inlet nozzle and the outlet nozzle.
The bobbin is fitted along the circumference of the
cylindrical sealing member, the protrusion is hermetically
fitted in one end of the cylindrical sealing member, and
the other end thereof is hermetically coupled with an
inner surface of the housing.
Further, an inlet valve seating surface and an outlet
valve seating surface are formed on the inlet nozzle and
the outlet nozzle respectively to seat the spool, and the
inlet valve seating surface and the outlet valve seating
surface are shaped to match with the spool, whereby the
first opening or the second opening is closed, when the
spool is seated on the inlet valve seating surface or the
outlet valve seating surface.
According to the preferred embodiment, the solenoid
valve further comprises a bushing provided between the
armature and the barrier wall for supporting the push rod.
To achieve the second object of the present
invention, there is provided a modulator for anti-lock
brake system comprising:
an electric motor;
first and second pumps driven by the electric motor
and provided into a modulator block;
first, second, third and fourth solenoid valves
installed into the modulator block for intermitting the
fluid flow in response to an electric signal;
first and second dampers provided into the modulator
block to be communicated with the respective outlets of
the first and second pumps for temporarily receiving the
fluid flowing out from the first and second pumps to
reduce the fluctuation of hydraulic pressure generated
from the first and second pumps; and
first and second accumulators provided into the
modulator block to be communicated with the respective
inlets of the first and second pumps for temporarily
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receiving the fluid flowing out from the first and second
solenoid valves and the third and fourth solenoid valves
to reduce the hydraulic pressure within the first to
fourth solenoid valves promptly,
wherein each of the first to fourth solenoid valves
comprises:
a valve body having a housing with a first port for
receiving fluid from a fluid generating source, a second
port for flowing in/flowing out the fluid and a third port
:LO for exhausting the fluid, and a cover hermetically coupled
to one end of the housing for closing the one end of the
housing;
a barrier wall for partitioning a chamber surrounded
by the housing and cover within the valve body into first
~5 and second chambers and having a first opening for
communicating the first chamber with the second chamber,
the first chamber being commlln;cated with the first port
and the second chamber being communicated with the second
and third ports;
~0 opening/closing means movable along lengthwise
direction of the valve body for alternatively opening and
closing the first opening and the third port in response
to an electric signal, and being positioned at a first
position of closing the third port and opening the first
~5 opening in a normal state that the electric signal is not
applied or at a second position of closing the first
opening and opening the third port in an active state that
the electric signal is applied, whereby the first port is
communicated with the second port or the second port i8
communicated with the third port; and
a solenoid assembly having an annular solenoid coil,
a bobbin wound by the annular solenoid coil and a pair of
electrodes electrically connected to the annular solenoid
coil and exposed to the outside of the valve body for
moving the opening/closing means to the second position
from the first position in response to the electric
signal.
Preferably, three O-rings are provided along the
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circumference of the first to fourth solenoid valves to
maintain the hermetical state between the first to third
ports while the first to fourth golenoid valves are
installed, whereby the installation of the first to fourth
solenoid valves is completed only by inserting them into
cylinders for a valve formed in the modulator block.
Further, each of the first and second dampers is
formed by a cylinder for a damper and a cover for a damper
in the modulator block, and each of the first and second
accumulators is formed by a cylinder for an accumulator,
a cover for an accumulator and a spring for accumulator in
the modulator block.
To achieve the third object of the present invention,
there is provided an anti-lock brake system for a vehicle
having at least one wheel provided with a wheel brake, a
brake pedal operable by the vehicle driver and a master
cylinder actuated by the brake pedal and having an outlet
connected to supply brake fluid to actuate the wheel
brake, the system comprising:
a wheel speed sensor provided to the wheel for
sensing the speed of wheel;
a pressure generating portion including an electric
motor and at least one pump driven by the electric motor
and having an inlet and an outlet;
a 2-position 3-way solenoid valve having a first port
communicated with both the outlet of the pump and the
master cylinder, a second port communicated with the brake
wheel cylinder and a third port communicated with the
inlet of the pump, the valve only movable between a first
position wherein the first and second ports are
communicated with each other to increase the pressure of
the brake wheel cylinder and a second position wherein the
second and third ports are communicated with each other to
decrease the pressure of the brake wheel cylinder;
a damper communicated with the outlet of the pump for
temporarily receiving the brake fluid flowing out from the
pump to reduce the fluctuation of hydraulic pressure
generated therefrom;
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an accumulator communicated with the inlet of the
pump for temporarily receiving the fluid flowing out from
the 2-position 3-way solenoid valve to reduce the
hydraulic pressure within the 2-position 3-way solenoid
valve promptly; and
control means for controlling the operation of the 2-
position 3-way solenoid valve to increase, decrease or
hold pressure of the brake wheel cylinder, the control
means receiving a speed signal from the wheel speed sensor
and outputting a valve-actuated signal having a
predetermined time period to the solenoid valve whereby
the solenoid valve is maintained in the first position or
the second position during the predetermined time period
in response to the valve-actuated signal,
the 2-position 3-way solenoid valve comprising:
a valve body having a housing with the first port for
receiving fluid from the pressure generating portion, the
second port for flowing in/flowing out the fluid and the
third port for exhausting the fluid, and a cover
~0 hermetically coupled to one end of the housing for closing
the one end of the housing;
a barrier wall for partitioning a chamber surrounded
by the housing and cover within the valve body into first
and second chambers and having a first opening for
communicating the first chamber with the second chamber,
the first chamber being commtlnicated with the first port
and the second chamber being communicated with the second
and third ports;
opening/closing means movable along lengthwise
direction of the valve body for alternatively opening and
closing the first opening and the third port in response
to an electric signal, and being positioned at the first
position of closing the third port and opening the first
opening in a normal state that the electric signal is not
applied or at the second position of closing the first
opening and opening the third port in an active state that
the electric signal is applied, whereby the first port is
communicated with the second port or the second port is
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communicated with the third port; and
a solenoid assembly having an annular solenoid coil,
a bobbin wound by the annular solenoid coil and a pair of
electrodes electrically connected to the annular solenoid
coil and exposed to the outside of the valve body for
moving the opening/closing means to the second position
from the first position in response to the electric
signal.
The valve-actuated signal may be a pulse-width-
modulation signal or a bang-bang control signal.
In the 2/3 solenoid valve according to the present
invention, the first and second ports are communicated
with each other, since the solenoid coil is de-energized
so that the spool closes the third port by a resilient
force of spring. When the solenoid coil is energized, the
spool is retracted by overcoming the resilient force to
open the third port and close the first port, so that the
second and third ports are communicated with each other.
The 2/3 solenoid valve according to the present
invention is simply constructed and has the reduced number
of component parts. Therefore, the possibility of
operational errors becomes low to enhance the reliability
of operation. Also, the response time of the 2/3 solenoid
valve becomes short, so that an anti-lock brake system
2S having the good performance can be constructed.
The modulator according to the present invention is
provided with four 2/3 solenoid valves and serves for
generating hydraulic pressure and intermitting the flow of
brake fluid in response to control signal from the control
means.
The modulator according to the present invention can
be assembled easily and has a compact design capable of
reducing the installation space of modulator and the
weight thereof, and hence, can be fabricated at a low
cost.
The anti-lock brake system according to the present
invention starts to operate on the basis of a speed signal
from the wheel speed sensor when a driver steps on the
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brake pedal. In an increase mode, the hydraulic pressure
generated from pump is supplied to brake wheel cylinder
through first and second ports of 2/3 solenoid valve
according to the present invention. At this time, the
solenoid coil is de-energized, because the 2/3 solenoid
valve is a normally open type. In a decrease mode, the
solenoid coil is energized to close the first port and
communicate the second port with the third port. If the
second and third ports are communicated with each other,
a part of fluid stored in the brake wheel cylinder is
transmitted to the accumulator through the third port, so
that the braking pressure i8 reduced. A hold mode is
acquired by repeating the opening/closing of the 2/3
solenoid valve under a PWM signal control or a bang-bang
control.
The anti-lock brake system according to the present
invention is simply constructed to reduce the possibility
of the erroneous operation, since one 2/3 solenoid valve
is assigned to one channel so that the number of solenoid
driven valves is reduced. Therefore, the anti-lock brake
system has the reliable braking characteristic.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and other advantages of the present
invention will become more apparent by describing in
detail preferred embodiments thereof with reference to the
attached drawings in which:
FIG. lA is a schematic view showing a hydraulic
system of a conventional anti-lock brake system utilizing
2/2 solenoid valve;
FIG. lB is a schematic view showing a hydraulic
system of a conventional anti-lock brake system utilizing
3/3 solenoid valve;
FIG. 2 is a sectional view of a 2/3 solenoid valve
according to a first embodiment of the present invention;
FIG. 3 is a sectional view of a 2/3 solenoid valve
according to a second embodiment of the present invention;
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FIG. 4 is a perspective view showing the inner
structure of a modulator for anti-lock brake system
provided with the 2/3 solenoid valve according to the
present invention;
FIG. 5 is a hydraulic circuit diagram of the
modulator according to the present invention;
FIG. 6 is an exploded view o~ the modulator according
to the present invention;
FIG. 7 is a constructional view of an anti-lock brake
system provided with the 2/3 solenoid valve according to
the present invention;
FIG. 8 is a graph showing the change of the pressure
of brake wheel cylinder with the lapse of time and being
acquired by testing an anti-lock brake system provided
with the 2/3 solenoid valve according to the first
embodiment of the present invention shown in FIG. 2; and
FIG. 9 is a graph showing the change of the pressure
of brake wheel cylinder with the lapse of time and being
acquired by testing an anti-lock brake system provided
with the 2/3 solenoid valve according to the second
embodiment of the present invention shown in FIG. 3.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the preferred first embodiment of a 2/3
solenoid valve according to the present invention will be
described in detail with reference to FIG. 2.
The 2/3 solenoid valve 100 according to this
embodiment includes a valve body 10 and a cover
hermetically coupled with one end of valve body 10.
Within valve body 10, a first chamber 44 and a second
chamber 46 are provided, in which first chamber 44 is a
space enclosed with cover 14 and a inlet nozzle 34 and
second chamber 46 is a space enclosed with inlet nozzle 34
and a outlet nozzle 36.
Within first chamber 44, a cover spring 16, a spring
supporting rod 22, an armature 24, a push rod 26 and a
bushing 32 are included. One end of cover spring 16 is
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supported by cover 14 and the other end thereof is
supported by armature 24 with spring supporting rod 22
inserted. Spring supporting rod 22 is fixed in the center
of one end of armature 24 a~d serves as a
supporting/guiding means of cover spring 16. Armature 24
is made of ferromagnetic materials and may be made of the
same materials as those of valve body 10. At the other
end of armature 24, push rod 26 is fi~ed.
Push rod 26 extends through bushing 32 and inlet
nozzle 34, and a spool 42 is integrally provided at one
end of push rod 26. Push rod 26 is fabricated with
armature 24 by pressing. Bushing 32 serves for supporting
push rod 26 and is provided with through holes through
which the fluid passes as well as an opening through which
push rod 26 is inserted. The shape and number of the
through holes are not especially limited as long as the
solenoid valve is operated smoothly. Spool 42
reciprocates axially to open and close inlet nozzle 34 or
outlet nozzle 36 alternatively. Push rod 26 and spool 42
are manufactured by cold rolling, for example, and
preferably, have Rockwell hardness of 60 to 65. One end
of spool 4Z landing on a outlet valve seating surface 37
has a hemispherical shape, and outlet valve seating
surface 37 is shaped to match with the one end of spool 42
landing thereon.
The diameter of inlet nozzle hole 38 is larger than
that of push rod 26 passing therethrough, so that a gap is
formed between inlet nozzle hole 38 and push rod 26.
Through the gap, first and second chambers 44 and 46 are
communicated with each other. Inlet valve seating surface
35 formed to inlet nozzle 34 is shaped to match with the
other end of spool 42 landing thereon, so that the fluid
flow through inlet nozzle 34 is blocked while landing of
spool 42.
2/3 solenoid valve 100 has a first port 20, a second
port 30 and a third port 40, first port 20 communicated
with first chamber 44 and second and third ports 30 and 40
communicated with second chamber 46. According to the
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embodiment, third port 40 is not formed to valve body 10
but provided to outlet nozzle 36 as a outlet nozzle hole
39. First port 20 is communicated with a master cylinder
82(see FIG. 7) of vehicle brake system, second port 30 is
communicated with brake wheel cylinders(not shown) mounted
to each wheel, and third port 40 is communicated with an
accumulator 66 or 68(see FIG. 5). In a normal state, in
which electric power is not supplied, spool 42 remains
landed on outlet valve seating surface 37 to close third
port 40, since 2/3 solenoid valve 100 is a normally open
type. Thus, in the normal state, the braking pressure
generated from master cylinder 82 is provided to the brake
wheel cylinder through first port 20, first chamber 44,
inlet nozzle 34, second chamber 46 and second port 30.
lS When a solenoid coil 12 is energized, the magnetic flux
generated from a solenoid assembly 11 permits armature 24
to overcome the resilient force of cover spring 16, so
that armature 24 is retracted toward cover 14.
Accordingly, spool 42 is forced to land on inlet valve
seating surface 35 formed on inlet nozzle 34 after being
separated from outlet valve seating surface 37 formed on
outlet nozzle 36, so that spool 42 is in a closing
position to close inlet nozzle 34. When spool 42 is in
the closing position, first port 20 is closed, third port
40 is opened and second and third ports 30 and 40 are
communicated with each other.
Solenoid assembly 11 is composed of a annular
solenoid coil 12 and a bobbin 13 wound with solenoid coil
12. Bobbin 13 is integrally formed by molding, for
example, in order to prevent the fluid from intruding in
solenoid coil 12 wound in bobbin 13. Further, solenoid
assembly 11 is fitted on the circumference of a
cylindrical sealing member 15, which serves for protecting
solenoid assembly 11 from the fluid being in first chamber
44 by means of sealing first chamber 11. Cylindrical
sealing member 15 consists of non-magnetic materials in
order to block the magnetic flux generated from solenoid
assembly 11. Electric terminals 18 are exposed to the
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exterior of valve body 10 and connected with conductive
wires each to energize solenoid coil 12.
In one end of cylindrical sealing member 15, a
protrusion 17 of cover 14 is inserted in order not to leak
the fluid. Protrusion 17 is shaped cylindrically to be
fitted in the inner surface of sealing member 15 and at
the center of protrusion 17, a hole 19 of which one end is
closed is formed to insert cover spring 16. One end of
cover spring 16 is supported on the closed end of hole 19
and the other end thereof is supported on armature 24, and
hence, armature 24 is pressed toward bushing 32 by a
predetermined force.
First, second and third O-rings 28, 28' and 28" are
provided to first and second U-shaped grooves 29 and 29~
and an L-shaped groove 31 formed on the outer surface of
valve body 10 to coaxially surround valve body 10. First,
second and third O-rings 28, 28' and 28" are provided for
maint~ini~g the hermetic state among first, second and
third ports 20, 30 and 40 when solenoid valve 100 is
installed in a modulator block 76(shown FIG. 6) for an
anti-lock brake system. Accordingly, when solenoid valve
100 is installed in modulator block 76, a space has a
substantially equal pressure, the space being communicated
with first port 20 and surrounded by first and second 0-
rings 28 and 28' mounted on each of first and second U-
shaped grooves 29 and 29', modulator block 76 and valve
body 10. Also, a space has a substantially equal
pressure, the space being communicated with second port 30
and surrounded by second O-ring 28' mounted on second U-
shaped groove 29', third O-ring 28" mounted on L-shaped
groove 31, modulator block 76 and valve body 10. Further,
a space has a substantially equal pressure, the space
being communicated with third port 40 and surrounded by
third O-ring 28" mounted on L-shaped groove 31, modulator
block 76, valve body 10 and outlet nozzle 36.
In FIG. 3, a 2/3 solenoid valve 100' according to a
second embodiment of the present invention is shown. In
the second embodiment, the same reference numerals as the
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first embodiment represent the same constituents. The
second embodiment is identical with the first embodiment
except that an orifice 52 and a first check valve 54 are
provided. Orifice 52 and first check valve 54 are mounted
in second port 30, preferably, with the opposing
positional relationship between each other. The hydraulic
pressure generated from a generating source is supplied
only through orifice 52. By a drop in pressure induced by
passing the fluid through orifice 52, the fluctuation of
hydraulic pressure in the brake wheel cylinder is almost
removed. First check valve 54 serves for shortening the
operating time of 2/3 solenoid valve 100' by the prompt
passage of the fluid, when second and third ports 30 and
40 are communicated with each other to transmit the fluid
from second port 30 to third port 40.
With reference to FIGs. 4 to 6, hereinafter a
modulator 200 for an anti-lock brake system being provided
with 2/3 solenoid valve 100 or 100' according to the
present invention will be described in detail. In the
drawings, Sl, S2, S3 and S4 designate first, second, third
and fourth solenoid valves, respectively and the valves
may be 2/3 solenoid valves shown in FIGs. 2 and 3.
In modulator block 76, a plurality of fluid passages
are formed for connecting each of constituents to transmit
the fluid therebetween. First passages Pl and Pl
communicate a primary master cylinder MCP(see FIG. 7) and
a secondary master cylinder MCS(see FIG. 7) with the
outlets of first and second pumps 58 and 60, respectively.
At each of branching points of first passages Pl and
Pl toward sixth passages P6 and P6, second and third check
valves 72 and 74 are provided in order that the hydraulic
pressure generated from primary and secondary master
cylinders MCP and MCS are not provided to the outlet of
first and second pumps 58 and 60.
First ports 20 and 20 of first and second solenoid
valves Sl and S2 are communicated with each other by one
second passage P2, and first ports 20 and 20 of third and
fourth solenoid valves S3 and S4 are communicated with
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each other by the other second passage P2. Third ports 40
and 40 of first and second solenoid valves Sl and S2 are
commllnicated with each other by one third passage P3, and
third ports 40 and 40 o~ third and ~ourth solenoid valves
S3 and S4 are communicated with each other by the other
third passage P3.
First and second accumulators 66 and 68 are
communicated with the inlet of each of first and second
pumps 58 and 60 by fifth passages P5 and P5, and first and
second dampers 62 and 64 are communicated with the outlet
of each of first and second pumps 58 and 60 by seventh
passages P7 and P7.
Second passages P2 and P2 are connected to third
passages P3 and P3 by fourth passages P4 and P4, and first
passages P1 and P1 are connected to second passages P2 and
P2 by sixth passages P6 and P6.
In modulator block 76, first, second, third and
fourth solenoid valves S1, S2, S3 and S4 according to the
present invention are installed to intermittently provide
the hydraulic pressure generated from first and second
pumps 58 and 60 to four wheels RR, FL, FR and RL. The
installation of first, second, third and four solenoid
valves S1, S2, S3 and S4 is completed only by inserting
them into valve-installing cylinders formed in modulator
block 76, since each of first, second, third and fourth
solenoid valves S1, S2, S3 and S4 is provided with first,
second and third 0-rings 28, 28' and 28"(see FIG. 2) to
maintain the hermetic state between the ports when
installing.
First and second dampers 62 and 64 are composed of
cylinders(not shown) for a damper formed in modulator
block 76 and a pair of damper covers 63, and first and
second accumulators 66 and 68 are composed of
cylinders(not shown) for an accumulator formed in
modulator block 76, a pair of accumulator covers 67 and a
pair of accumulator springs 69.
First and second dampers 62 and 64 retain temporarily
the fluid flowing out the outlet of first and second pumps
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58 and 60 to reduce the fluctuation of hydraulic pressure
caused by first and second pumps 58 and 60.
When the fluid within second chambers 46 of first and
second solenoid valves S1 and S2 flows out third ports 40
thereof to reduce the hydraulic pressure of brake wheel
cylinder, first accumulator 66 retains temporarily the
fluid flowing out third ports 40, so that the hydraulic
pressure of second chamber 46 of first and second solenoid
valves S1 and S2 is reduced promptly. When the fluid
within second chambers 46 of third and fourth solenoid
valves S3 and S4 flows out third ports 40 thereof to
reduce the hydraulic pressure of brake wheel cylinder,
second accumulator 68 retains temporarily the fluid
flowing out third ports 40, so that the hydraulic pressure
of second chamber 46 of third and fourth solenoid valves
S3 and S4 is reduced promptly.
The hydraulic pressure generated from first pump 58
is provided to first ports 20 of first and second solenoid
valves Sl and S2 through first passage Pl, second check
valve 72, sixth passage P6 and second passage P2. The
hydraulic pressure generated from second pump 60 is
provided to first ports 20 of third and fourth solenoid
valves S3 and S4 through first passage Pl, third check
valve 74, sixth passage P6 and second passage P2.
FIG. 7 is a constructional view of an anti-lock brake
system 300 composed of 2/3 solenoid valve 100 or 100' and
modulator 200 according to the present invention.
Anti-lock brake system 300 according to the present
invention is for the brake system of the diagonal split
type that one front wheel and the diagonally opposite rear
wheel are assigned to each of two master cylinders, but it
is especially limited to this type. To promote the
understanding, FIG. 7 shows only the hydraulic pressure
circuit diagram including primary master cylinder MCP and
rear right and front left wheels RR and FL.
On wheel RR and FL, first and second wheel speed
sensors 92 and 94 are installed respectively and the speed
signal outputted therefrom is inputted to an ECU 90 for
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19
controlling the operation of anti-lock brake system 300.
First, second, third and fourth solenoid valves S1, S2, S3
and S4 and a motor for driving first and second pumps 58
and 60 are connected to the output of ECU 90.
With reference to the drawings, hereinafter the
operation of 2/3 solenoid valve according the present
invention and anti-lock brake system having the 2/3
solenoid valve will be described.
In a normal state that anti-lock brake system is not
operated, the hydraulic pressure generated from primary
and secondary master cylinders MCP and MCS is provided to
the brake wheel cylinders, each of them being installed on
the respective four wheels RR, FL, FR and RL, after
passing through first and second ports 20 and 30
successively, if a driver steps on a brake pedal 80. When
anti-lock brake system 300 is operated, motor driving
signal is outputted from ECU 90 to drive motor 56 and
valve opening/closing signal is outputted from ECU 90 to
opentclose first and third ports 20 and 30 of each of
first, second, third and fourth solenoid valves S1, S2, S3
and S4 in accordance with a predetermined algorithm stored
in ECU 90, whereby the braking pressure is increased, held
or decreased.
In an increase mode, the hydraulic pressure generated
from ~irst and second pumps 58 and 60 is provided to first
passages P1 and P1 and thereafter, passes through the same
path as in the normal state that anti-lock brake system is
not operated, so that the braking pressure is increased.
Since 2/3 solenoid valve according to the present
invention is a normally open type, in the de-energized
state of solenoid coil 12, spool 42 is landed on outlet
valve seating surface 37 by the resilient force of cover
spring 16 to close third port 40 and hence, the hydraulic
pressure generated from first and second pumps 58 and 60
is provided to the brake wheel cylinders via the same path
as in the normal state. Each of first and second dampers
62 and 64 is disposed at the outlet of first and second
pumps 58 and 60 to reduce the fluctuation caused by the
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pumping operation of first and second pumps 58 and 60.
In a decrease mode, solenoid coil 12 is energized to
generate the magnetic flux, 80 that armature 24 overcomes
the re6ilient force of cover spring 16 to be retracted
toward cover 14. Spool 42 is separated from outlet valve
seating surface 37 and landed on inlet valve seating
surface 3S, so that third port 40 is opened and first port
20 is closed. Therefore, the fluid in the brake wheel
cylinder is exhausted toward first and second accumulators
66 and 68 through second and third ports 30 and 40,
thereby decreasing the braking pressure.
A hold mode is performed by operating spool 42
repetitively by means of utilizing a pulse width
modulation or a bang-bang control. If solenoid coil 12 is
energized and de-energized, repetitively, first and second
ports 20 and 30 are opened/closed repetitively by the
movement of spool 42, thereby keeping the braking pressure
constant.
FIG. 8 is a graph for showing the relationship
between the pressure of the brake wheel cylinder and the
time, the graph being acquired by testing anti-lock brake
system 300 provided with 2/3 solenoid valve 100 according
to the first embodiment of the present invention shown in
FIG. 2. FIG. 9 is a graph for showing the relationship
between the pressure of the brake wheel cylinder and the
time, the graph being acquired by testing anti-lock brake
system 300 provided with 2/3 solenoid valve 100' according
to the second embodiment of the present invention shown in
FIG. 3.
With reference to FIGs. 8 and 9, the horizontal axis
is a time axis and the vertical axis is a pressure axis.
Further, "a" represents the change of the pressure in
brake wheel cylinder and "b" represents the waveform of
the signal supplied to solenoid valve. As shown, the
increase mode is accomplished by OFF signal, the decrease
mode is accomplished by ON signal and the hold mode is
accomplished by pulse-width modulation signal in which ON
and OFF signals are repeated with a predetermined time
CA 02202973 1997-04-17
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period.
In FIG. 8, it can be seen that the fluctuation of
about 10 to 20 bar takes place in the hold mode and the
fluctuation of about 5 to 10 bar takes place in the
increase mode. The fluctuation may induce trouble for
master cylinder and the unstable operation of anti-lock
brake system. As shown in FIG. 9, the fluctuation is
almost removed by utilizing 2/3 solenoid valve 100' shown
in FIG. 3 according to the second embodiment of the
present invention.
The 2/3 solenoid valve according to the present
invention is simply constructed and has the reduced number
of component parts. As the result, the possibility of
operational errors becomes low to enhance the reliability
of operation. Also, the response time of the 2/3 solenoid
valve becomes short, so that an anti-lock brake system
having the good performance can be constructed.
The modulator according to the present invention can
be assembled easily, has a compact design capable of
reducing the installation space of modulator and the
weight thereof, and hence, can be fabricated at a low
cost.
The anti-lock brake system according to the present
invention is simply constructed to reduce the possibility
of the erroneous operation, since one 2/3 solenoid valve
is assigned to one channel so that the number of solenoid
driven valves is reduced. Therefore, the anti-lock brake
system has the reliable braking characteristic.
While the present invention has been particularly
shown and described with reference to particular
embodiment thereof, it will be understood by those skilled
in the art that various changes and modifications may be
effected therein without departing from the spirit and
scope of the invention as defined by the appended claims.
